The present invention refers to an illumination device or exposure device for producing models, such as reticles and masks, used for manufacturing electronic elements, or for direct illumination of wafers and substrates during the photolithographic steps required for production, or for direct illumination of structures including light-sensitive layers, said illumination or exposure device comprising a light source and a pattern generator.
The present invention especially deals with the production of models, reticles and masks, or with direct illumination in the micrometer range in the fields of semiconductor production, the production of integrated circuits, hybrid production and the production of flat screens as well as similar production methods in the case of which illumination processes are used. The present invention especially concerns an illumination device, which is adapted to be used for direct illumination of semiconductor wafers in the field of semiconductor production and for direct illumination of substrates in the field of hybrid and bonding technology.
For the production of reticles, which are illumination templates for the photolithographic production of circuits, as well as for the production of masks and for direct illumination of semiconductor products, electron beam writers, laser beam units and optical pattern generators including a laser light source or a mercury-vapour lamp are used. Optical pattern generators according to the prior art produce the desired structures by carrying out successive, individual illuminations of rectangular windows, which are defined by mechanical rectangular shields. The complexity of the structure to be produced determines the number of illumination rectangles required, and said number, in turn, determines the writing time or the exposure time for the structure. The accuracy of the structures which can be produced by these known pattern generators is, in turn, limited by the accuracy of the mechanical rectangular shields used.
In the case of laser beam units according to the prior art, the surface to be illuminated is rastered by a laser beam. The writing speed or illumination speed of such laser beam units is limited due to the serial data flow required for the rastering process. In addition, such laser beam units necessitate high mechanical-optical investments.
The electron beam units employed in the prior art can only be used for the illumination of electron-sensitive, special photoresist systems, and, in comparison with the above-described laser beam units, they additionally require the use of a high-vacuum technique. It follows that electron beam units necessitate very high capital expenditure and operating costs.
The technical publication B. W. Brinker et al, "Deformation behavior of thin viscoelastic layers used in an active, matrix-addressed spatial light modulator", Proceedings of SPIE 1989, vol. 1018, already discloses the use of a reflective optical Schlieren system including an active, matrix-addressed, viscoelastic surface light modulator for the purpose of producing television pictures or for the purpose of image display. This surface light modulator includes a permanent light source whose light falls vertically onto the surface of the surface light modulator through an appropriate optical system. Surface areas of the surface light modulator are adapted to be deformed in response to addressing of control electrodes so that the light falling onto the surface will be reflected as diffracted light in the case of addressed surface elements and as undiffracted light in the case of non-addressed surface elements. The undiffracted light will be returned to the light source, whereas the diffracted light will be used via the optical Schlieren system for image production on the television screen or on an image display area.
The company publication of the firm of Texas Instruments, JMF 008:0260; 10/87, discloses a surface light modulator whose reflective surface consists of a plurality of electrically addressable, mechanically deformable reeds.
The applicant's prior, not-prepublished international patent application now U.S. Pat. No. 5,296,891 discloses an illumination device for producing models used for manufacturing electronic elements, or for direct illumination of wafers or substrates, comprising a light source and a pattern generator, said pattern generator including an optical Schlieren system and an active, matrix-addressable light modulator, which has a reflective surface whose addressed surface areas diffract incident light and whose non-addressed surface areas reflect incident light, said Schlieren system comprising a Schlieren lens, which is arranged close to the surface light modulator, and a projection lens, a filter device being arranged between said Schlieren lens and said projection lens, said filter device filtering out the light of non-addressed surface areas and permitting only the diffracted light of addressed surface areas of the surface light modulator to pass via the projection lens to the model and the electronic element, respectively. This illumination device operates in the positive mode, where the addressed areas of the surface light modulator correspond to exposed areas in the projection on the model and the electronic element, respectively. In other words, the filter device of this illumination device permits all orders of diffraction to pass, with the exception of the zeroth order. The intensity distribution of the projection shows an undesired modulation whose amplitude and modulation period depend on the number and on the nature of the orders of diffraction contributing to the projection as well as on the relative influence of the individual orders, the intensity contribution of one order of diffraction being propotional to the respective Bessel function raised to the power of two. The period of the fine structure of the projection must therefore be reduced to such an extent that it will no longer be resolved by the imaging optics nor by the photoresist to be exposed. For this purpose, it will, for example, be possible to minimize the grating constant of the surface light modulator, to reduce the projection scale, or to increase the so-called diffraction efficiency, whereby the influence of higher orders of diffraction will be increased. In view of the fact that an increase in the deformation amplitude is necessary for increasing the diffraction efficiency, this will entail an increased grating constant so that the desired effect will partly be nullified again. Hence, only a limited degree of homogeneity of the illumination of the individual pixels of the projection can be achieved by means of this illumination device.
U.S. Pat. No. 4,675,702 discloses a surface illumination device, which can be used e.g. for illuminating photosensitive films and which can be constructed as a "photoplotter". This illumination device comprises a light source for generating an essentially parallel light bundle falling through a controllable light matrix valve, which can, for example, be formed by a liquid-crystal layer, whereby areas of the photosensitive film which are not to be exposed will be defined.
U.S. Pat. No. 4,728,185 deals with a Schlieren imaging system, which can be used with light modulators in an optical printer. The light valves themselves can consist of electronically addressable surface light valves. The light valve disclosed in this publication is a bar-type light valve, but not an area-like one. Furthermore, the known illumination device is arranged such that only the parts of the bar-type light modulator which are addressed will be imaged on a photosensitive layer.